Part 9

“You will notice that the waning of day between photographs Nos. 17 and 18 has produced a remarkable change in the appearance of Tycho. Since the Full Moon phase Tycho has resembled a button rather than a volcanic crater, but now it has once more assumed the form of a very beautiful ring with its central peak clearly shown, its western wall, bright and its eastern wall casting a broad, black shadow. Most of the rays have now disappeared, only two or three, running over the eastern hemisphere, remaining visible. The immense walled plains near Tycho have again become prominent, Maginus toward the southwest, Clavius toward the south, and Longomontanus toward the southeast being the most conspicuous. Clavius is always a wonderful object for the telescope, but it is rather more interesting in the lunar morning than in the evening. Away over near the eastern limb, where the sun is still high, Grimaldi shows its dark oval, with a couple of mountain peaks on its western rampart shining brilliantly. The small, dark spot below it, toward the east, is in the walled plain, Riccioli. The bright spot with starlike rays, a long way south of Grimaldi, and east of the _Mare Humorum_, is Byrgius, a walled plain near which exists a small system of bright streaks resembling those surrounding Copernicus and Kepler, but much less extensive.”

“Do you recall my expression of impatience this morning when you were giving me the names of a long string of crater rings?” said my friend, smiling. “Well, I am now going to make a confession. Perhaps it is slightly of a penitential nature. I find now that these names, although they certainly are far from picturesque in most cases, begin to interest me, because, I suppose, I understand better the character and meaning of the things that they represent. The ceaseless Latin terminations no longer annoy me, for I do not think of them, but of the things themselves.”

“It is always so,” I replied, “whenever one takes up a new study. I know that you have dipped a little into botany, and I am sure that the Latin names which abound in that science must have repelled you at first. But after a time, when you had begun to recognize the beautiful flowers and the remarkable plants for which they stood, you found that even these names assumed a new character and became interesting and memorable. You will find it the same if you continue to study the moon. The most stupid designations will derive interest from their applications.”

“Yes, that is no doubt true. Still, I wish that Riccioli had possessed a little more imagination.”

“Be thankful, then, that he did not name the lunar ‘seas’ and ‘bays.’ You must now bid good night to your ‘dark woman.’ You observe that the _Mare Nubium_ is beginning to fall under the shadow, and that her features are growing indistinct. If you will turn the photograph upside down you will find that the Moon Maiden has retired. She belongs exclusively to the western hemisphere, and it is only the eastern hemisphere of the moon that now remains visible to us, for we are close to the phase of Last Quarter. This is an aspect of the moon with which you may not be very familiar. To see the moon at Last Quarter, and particularly after she has passed that phase, we must rise near midnight and devote the early morning hours to observation. During these later phases, however, one may see the moon in the heavens during the daytime all through the forenoon and a part of the afternoon. She is a very beautiful object then, although few persons, I fear, ever take the trouble to look at her. The lighter parts of her surface assume a silvery tint in the daylight, and the dark plains seem suffused with a delicate blue from the surrounding sky. Exquisite views of the moon may then be obtained with a telescope. The glare of reflected light from the mountains and crater rings, which dazzles the eye at night, is so reduced that the telescopic image becomes beautiful, soft, and pleasing. The same principle has been very successfully applied in recent years to the study of the planet Venus. Her atmosphere is so abundant, in contrast to what we find on the moon, that she is as blinding in a telescope as a ball of snow glittering in full sunshine; but when seen in the daytime, her features, indistinct at the best, may be more clearly discerned.”

“Oh, you interest me deeply! If Venus is supplied with such an abundance of air, I suppose she is inhabited?”

“It is not exactly orthodox among those calling themselves astronomers to talk of inhabitants on the planets, but I do not mind telling you privately that I think that Venus is most likely a world filled with all kinds of animate existences. Our present business, however, is with the moon, and I must recall your attention to the photographs. We shall next take up No. 19. Here the crescent shape becomes again evident, but reversed in position as compared with the crescent of the new and waxing moon. Only two of the ‘seas’ now remain completely in view—the _Mare Humorum_ and the _Oceanus Procellarum_.”

“That term I think you have translated as the ‘Ocean of Tempests.’ Pray, do you know any reason why it should have been thus named?”

“There is not the slightest reason that I know of. You must ascribe it to the vivid imagination of that old astronomer whom you so greatly admire. I regret, sometimes, that he cannot be here to explain to you the thoughts that occupied his mind. They must surely have been very captivating, even though not very scientific. Remark that there are many of the features of the eastern part of the moon which we can now discern more clearly than in any of the preceding pictures. Beginning at the top we see the vast inclosure of Longomontanus with the top of its encircling walls illuminated, while the interior is all in deep shadow. Its western rampart projects into the night and seems detached from the main body of the moon. Along the terminator below Longomontanus, what appears to be another immense walled plain presents a similar aspect. This, however, consists of several smaller formations grouped near together, only their loftiest points being illuminated. The steep borders of the _Mare Humorum_ are finely shown. Notice how the floor of that little ‘sea,’ which is about the size of England, as Mr. Elger has remarked, is mottled with whitish spots, and how distinct the ring of Gassendi appears at the northern end of the _mare_. You can even see the comparatively small crater that crowns the northern wall of the ring. Southeast of the _Mare Humorum_ are visible the great flat plains of Schiller and Schickard. Notice also how all the surface of the moon in that direction is freckled with crater pits, which resemble the impressions made by raindrops in soft sand. But the smallest of these pits is larger than the greatest volcanic crater on the earth.

“The _Oceanus Procellarum_ is beautifully illuminated in this picture. In several places, particularly north of the _Mare Humorum_, parts of _submerged_ rings are visible. These are great curiosities, and we shall see more of them elsewhere. Some selenographers believe that they are the remains of an earlier world in the moon, which was buried by a tremendous upheaval and outrush of molten material from the interior. You will remember, perhaps, that I spoke of a catastrophe of that kind when pointing out the half-buried ring of Fracastorius at the southern end of the _Mare Nectaris_.”

“Did that catastrophe occur after the formation of the huge lunar volcanoes?”

“It is difficult to say just when it occurred, but the appearances generally favor the view that it was subsequent to the great volcanic age. It is the opinion of Mr. Elger, whom I have once or twice mentioned as an English observer who has devoted special attention to the study of the moon’s surface, that the _mares_, as we now see them, do not represent the original beds of the lunar oceans. These beds, which, according to this view, were at first deeper, have been covered up, at least over a great part of their areas, by the outrush of molten lava. If they were ever filled with water it was very likely prior to that occurrence. But you must remember that all this is speculation, very interesting, it is true, but based upon insufficient data to enable us to be sure of our conclusions. I shall show you later that some recent students of lunar phenomena have formed the opinion that there is a strong argument to be drawn from geological analogies in favor of the view that the lunar _mares_, practically in the state in which we see them, have been true sea beds.

“Let us continue our inspection of photograph No. 19, which is one of the most interesting of the series. Look at the crater ring Kepler, in the midst of the _Oceanus Procellarum_. We have not before seen it in the aspect which it now presents. Hitherto it has appeared only as a bright point surrounded by a light patch covered with radiating streaks. But now, with the late afternoon sunlight striking across it, its walls are illuminated in such a manner that its very perfect ring shows very clearly, about half of the interior lying in shadow, which serves to give it a striking relief. If we suppose a time when the _Oceanus Procellarum_ was a real ocean, and when Kepler was an active volcano rising above its waters, its situation, far from all shores, would have been not unlike that of the great volcano of Kilauea in the Hawaiian Islands. In that case we might assume that the streaks around it represent ancient lava flows, which spread far about over the bed of the ocean. The same explanation would apply to the streaks and rays around Copernicus, and half a dozen other similar ring mountains.

“You will also observe that the afternoon slant of the solar rays has considerably changed the appearance of Aristarchus. Now for the first time the crateriform shape of that most remarkable mountain has become evident on account of the shadow in the interior. This shadow has almost reached the central peak which is the brightest part of the entire formation. You may be interested in the fact that the brilliance of the central peak of Aristarchus is so great that it stands in an order by itself, in what may be called the photometry of the moon’s surface. Ten orders of relative brightness have been adopted to represent the various reflective powers of different parts and spots of the moon. I copy them from Mr. Elger’s list. They are as follows:

“0° = Black (example, the shadows of mountains).

“1° = Gray black (example, darkest places in the walled plains of Grimaldi and Riccioli).

“2° = Dark gray (example, the floor of Endymion).

“3° = Medium gray (example, interior of Theophilus).

“4° = Yellowish gray (example, interior of Manilius).

“5° = Pure light gray (example, surface around Kepler).

“6° = Light whitish gray (example, walls of Macrobius).

“7° = Grayish white (example, Kepler).

“8° = Pure white (example, walls of Copernicus).

“9° = Glittering white (example, Proclus).

“10° = Dazzling white (sole example, the central peak of Aristarchus).”

“Really, I am greatly surprised by what you tell me,” said my friend. “I would never have imagined that there were so many different neutral tints on the moon.”

“You would be still more surprised,” I replied, “if I could present to you a similar table of the different tints of color that have been discovered there. But I am not aware that any scale of lunar colors has been prepared. There are, however, various shades of brown, yellow, and green. Most of them are found in the _mares_ and walled inclosures. Some of them appear to be variable, and some are only to be detected under particular illuminations.”

“Are not such colors an indication of something living there?”

“It may be so—an indication, for instance, of the existence of ‘lunar grass,’ the mention of which so amused you a little while ago.”

“Oh, it was not the ‘grass’ that amused me, but your unexpected way of introducing it. I _want_ to be convinced that there is grass there, and a great many other things besides grass. But I am not yet satisfied concerning that unique peak in Aristarchus. ‘Dazzling white’ you say is its description in the scale of tints. That excites my curiosity immensely. I think you have told me already that it cannot be snow, but you have spoken of the possibility of crystals and of metal. Do you know, I like the idea of ascribing the phenomenon to metal. It recalls something that I read in childhood about the first discoverer of a silver mine in Mexico. As I remember the story, an Aztec hunter, chasing his game across a mountain, seized upon a bush to aid him, and the roots giving way disclosed a glittering mass of silver. Why not let me imagine that the peak of Aristarchus is composed of pure silver?”

“There is no harm in imagining that if you wish to do so. But then your imagination, or rather your knowledge, should go a little farther and recall the fact that silver does not remain dazzling bright when exposed.”

“Ah, but you say there is no air, no water, no rains, no moisture on the moon. Under such circumstances might not a metal remain bright?”

“It is possible, but I hardly think that it would. It is likely that other corroding influences exist. A better explanation, I think, is afforded by supposing that the reflecting surface is simply composed of a rocky mineral, resembling in its power of reflection a mass of quartz crystals or imbedded planes of mica. There is no absolute impossibility involved in thinking that it may be simply white rock.”

“Why not say marble—a gigantic Carrara mountain on the moon?”

“I fear that that would involve a geological history for the lunar world for which we have not sufficient warrant in observed facts. I prefer to assume a volcanic origin for the phenomenon. Since you are so interested in the mystery of Aristarchus I may add that a part of the floor and the inner side of the ring are also extremely bright, but not quite so bright as the central peak. That alone stands at the top of the scale. Putting the peak at 10°, Mr. Elger finds that the other brilliant parts of Aristarchus possess only 9½° of brightness. Yet the whole interior is so glistening that when the sunlight falls vertically it almost resembles the inside of a crystal cup, and details are hidden in the glare.

“Now please look at the ‘Bay of Rainbows’ in the photograph before us. Cape Laplace at its western end lies close to the terminator and appears as a minute speck of light. The great bow-shaped shore is clearly defined, the level surface within being very dark and the highlands around it comparatively bright. The crater mountain Bianchini you will recognize near the center of the bow. Several other similar crateriform mountains are visible toward the north and east. In this light the surface of the moon eastward from the North Pole appears as rough and broken with craters and crater plains as we saw in the earlier pictures that it is toward the west.

“Before directing our attention to photograph No. 20, let us return for a moment to Aristarchus. When speaking of that formation a few minutes ago I interrupted myself in order to give you the scale of tints on the moon, which demonstrated the unique brilliance of the peak inclosed by the ring. I intended to point out to you then the fact that in photograph No. 19 we see, for the first time, not only the ring of Aristarchus but its curious neighbor Herodotus. A light streak, which we observed in an earlier picture, seems to connect the two. It is better, however, to notice this now because in turning from No. 19 to No. 20 you will perceive once more a change in the appearance of Aristarchus and its neighborhood. In No. 20 Aristarchus is distinctly more conspicuous. The night has advanced during almost exactly twenty-four hours, having in the meantime swept across the entire length of the ‘Bay of Rainbows,’ which we now no longer see. If we had been using a telescope during that interval we should have beheld a very interesting spectacle, for sunset on the ‘Bay of Rainbows’ is quite as remarkable, although in a very different way, as sunset on the Bay of Naples. The astronomer, seated amid the lonely gloom of his observatory dome, and watching the change of light and illumination on the surface of the moon, has many an hour of solitary enjoyment of aspects of nature that are quite impossible on the earth, and that frequently lure him into poetic meditations which find no place in his notebook.”

“I am very glad to hear you say that. It enhances my opinion of the astronomers, and convinces me that after all they are not so severely scientific as they describe themselves.”

“If they were,” I replied, “or if all of them were, it would be a bad augury for the future of their science. Do not think that in occasionally seeking to restrain your imagination I wish to express condemnation of what, after all, is the noblest of human faculties. But again we are forgetting our principal business, which is with the facts. Aristarchus, as I have said, has undergone another distinct change of appearance from that which it showed before. The central peak is now covered by the shadow of the eastern wall, but still the reflection from the western wall alone is sufficient to make it the brightest spot on the moon. Herodotus, on the other hand, has become indistinct and the Harbinger Mountains are practically invisible, but we can detect the existence of the enormous chasm or cañon, which I told you once issues from the interior of Herodotus and goes winding nearly a hundred miles over the floor of the _Oceanus Procellarum_.

“Notice, also, how clearly visible three or four relatively small craters east of the ‘Bay of Rainbows’ have become, and how conspicuous are several large walled plains on the northern ‘horn.’ The dark level south of these formations and between them and the small craters has also a name which I have not before mentioned. It is the _Sinus Roris_, ‘Gulf of Dew.’ It connects the _Mare Frigoris_ with the _Oceanus Procellarum_. It is another legacy from your friend the imaginative astronomer.”

“Then once more he receives my thanks for having done his best to make the moon an ideal world. It is always painful to have one’s ideals destroyed.”

“I hope that I have not been destroying any of yours.”

“No, but at least you have caused a change in my impressions about the character of the moon. Henceforth there will be an element of terror as well as of unexpected grandeur mingled with my thoughts of the ‘Queen of Night.’”

“That element will not be diminished by what I am about to point out. Look far over near the eastern border of the _Oceanus Procellarum_, directly east of Aristarchus. There you will distinguish the outlines of two or three vast submerged ring plains, which we may regard as relics of that earlier lunar world, which preceded the outgush of lava that Mr. Elger thinks covered the sea bottoms. Observe also the singular light streak that runs from Kepler, now barely visible at the edge of night, to a dark little crater, beyond which lies a bright point off the coast of the ‘ocean.’ South of this there are other submerged ring plains, one of which, named Letronne, has a high western wall, which forms in the picture a sort of promontory projecting from the southern border of the _Oceanus Procellarum_, almost directly north of Gassendi. The latter is very clearly shown at the lower end of the _Mare Humorum_, the western side of which is in shadow, while its whole surface has turned very dark. On the southern horn of the crescent the ring plains, Schickard and Schiller, are still prominent, and the northern and eastern edges of the _Mare Humorum_ appear more ragged with mountains and crater rings than before.”

“And have all these mountains and craters names?”

“Not all of them, but many more, perhaps, than you suppose. On the whole visible surface of the moon about 500 objects, not including the ‘seas,’ have received names. It may surprise you to learn that the position of the most important of these objects has been ascertained with an accuracy which is still lacking in our determination of positions on the earth. In other words our charts of the moon are more exact than those of our own planet.”

“That does indeed surprise me. I should have thought that, living on the earth, we could make very correct maps of it, while, as for the moon, two or three hundred thousand miles away, it seems to me not so easy to do that.”

“It is mainly because we are on the earth that we find such great difficulty in making accurate maps of it. We cannot look at the earth as a whole, but we have to crawl over its surface, making measurements as we go, and afterwards translating those measurements into lines and angles on paper. Thus we are still uncertain about the precise distance between many important points on our globe, while for points on the moon no corresponding uncertainty exists. The moon hangs before us in the sky, with no clouds except those in our own atmosphere to obscure it, and it is only necessary carefully to observe the position of particular points, and with the proper instruments to measure their distance and directions from one another. But even this is not a thing that can be accomplished without much pains and much knowledge. The astronomer, no matter what field he chooses, is necessarily a hard worker, and his motto, above everything else, is accuracy. No one is more tempted than he by the sublimity and the extraordinary character of the objects of his study, to give rein to the imagination, and yet imagination is the thing of all others from whose vagaries he must most carefully guard himself. So you must not blame him too severely if he has not dotted the shores of the moon with cities, and populated its plains with industrious farmers.”

“If you will permit me to wander a little aside from our photographic studies for a few minutes,” said my friend, “I should like to ask you about two or three things concerning the moon which have long puzzled me. From my earliest days, living the greater part of the time in the country, I have heard that the moon exercises a decided influence over the weather, and over the growth of vegetation. I have neighbors who would never think of planting certain things except ‘in the New of the moon’! Some will not cut timber except ‘in the Old of the Moon,’ as they say that the sap is drawn up by the moon’s influence when she is growing. Is there really any truth in all this?”

“Not the least. At any rate there is no scientific evidence whatever for such statements, and no probability that they are based on facts. They are the result of faulty observation, misled by coincidences. It is _imaginable_ that the light of the moon might have some influence upon vegetable growth if it were an original kind of light coming from the moon herself. But moonlight is only reflected sunlight, and when we examine it with the spectroscope we do not find that the rays of light in visiting the moon and returning thence to the earth have had either anything added to or anything taken away from them, except intensity. The total amount of light reflected from the moon upon the earth is estimated to be about 1/618000 of the total amount that comes to us from the sun. Curiously enough the moon appears to reflect proportionally more heat than light, the amount of lunar heat received by the earth being reckoned at 1/185000 of the amount coming from the sun. The popular idea that the moon affects the movement of sap in plants is equally illusory.”

“But about the weather? I know people who believe that a change of the moon from one phase to another brings about a change of weather. Is that true?”